It has long been recognized that the rate and regularity of the heartbeat reflect the physiological condition of the heart. Studies have indicated that variations in the heart action also give warning in many instances of impending heart trouble.
The electrocardiograph gives a good and accurate tracing of heart action, but its use is restricted to the medical office and to those patients whose history or symptoms indicate that a special heart test should be made.
For greater utility and effectiveness a portable device is needed which can be operated by the subject himself in a wide variety of conditions. Joggers or cardiac sufferers, for instance, need to measure their pulse rates periodically in order not to exceed some maximum rate specified by their physicians. A portable instrument useable during periods of activity could provide a means for the determination of safe limits on exercise or other forms of stress.
Such a device must be accurate and easy to use and it should preferably provide a read-out means which is immediately recognizable. It should not be necessary, for example, to count pulses or make calculations or conversions which require time and concentration and are subject to human error.
In order to sense irregularities in the heartbeat as well as the average rate, the device should be capable of taking measurements over relatively brief periods covering no more than a few beats. Readings should be continually repeated to indicate variations.